ResearchSpace :: Browsing by Author "Johakimu, Jonas K"

Browsing by Author "Johakimu, Jonas K"

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Beneficiation of pulp mill waste green liquor dregs: Applications in treatment of acid mine drainage as new disposal solution in South Africa
(Elsevier, 2020-02) Sebogodi, Keolebogile R; Johakimu, Jonas K; Sithole, Bishop B
Acid mine Drainage (AMD) is a low pH, sulphate and heavy metal rich leachate that is produced from oxidation of sulphide bearing minerals commonly found in the host rocks of some mineral ores. The pH augmentation, and sulphate and metal removal in AMD is often achieved by adding alkaline reagents in it. CaCO3 and/or its derivatives are commonly used for this purpose due to their abundance and affordability as compared to other neutralizing reagents. The problems associated with the use of this naturally occurring reagent do not only include the emission of greenhouse gases and ecological disturbances but also include a disastrous implication of depleting their reserves. To avoid these predicaments, green liquor dregs (GLD) from two Kraft pulp manufactures in South Africa were used as alternative alkaline reagents to neutralize AMD originating from Witwatersrand goldfields in Johannesburg. These GLD samples were referred to as GLD A and B. CaCO3 was used as a reference material. The GLD samples had neutralizing values that are comparable to that of CaCO3. Thus, CaCO3, GLD A, and GLD B had a neutralizing value of, 26.0, 21.2, and 21.0 % CaO respectively. Different dosages 1, 2, 6, 10, and 20 g/L of these neutralizing reagents were used to neutralize the AMD. Results of this study showed that raising the pH of AMD was possible even at a low dosages of 1 g/L. At this dosage, the acidity of the AMD sample changed from 183.36 to 21.7, 36.4, and 48.72 mg/L CaCO3, and changed the pH from 5.6 to 8.84, 8.21, and 8.0 respectively. However, the SO42- and Ec had increased from 2093 to 2360, 2538, and 2407 mg/L and from 3.6 to 4.0, 4.3, 4.2 mS/cm respectively, indicating that caution should be taken to keep these values low by keeping the reagent dosage low and being cognizant of the carbonate mineral present in GLD. The x-ray diffraction patterns of the reacted samples confirmed the presence of metal oxides and Ca and Mg compounds that were depicted by SEM/EDX micrographs. In conclusion, the results from this study showed that the pH of AMD can be raised to optimum pH process value and reduce the acidity at a low dosage, a competitive advantage over commercial CaCO3. The proposed concept can be adopted by both the mining and pulp and paper industries, for the upscaling of co-disposing GLD and AMD contaminants as an eco-friendly alternative for the CaCO3.
Beneficiation of pulp mill waste green liquor dregs: applications in treatment of acid mine drainage as new disposal solution in South Africa
(Beneficiation of pulp mill waste green liquor dregs: applications in treatment of acid mine drainage as new disposal solution in South Africa, 2019-10) Sebogodi, Keolebogile R; Johakimu, Jonas K; Sithole, Bishop B
Acid mine Drainage (AMD) is a low pH, sulphate and heavy metal rich leachate that is produced from oxidation of sulphide bearing minerals commonly found in the host rocks of some mineral ores. The pH augmentation, and sulphate and metal removal in AMD is often achieved by adding alkaline reagents in it. CaCO3 and/or its derivatives are commonly used for this purpose due to their abundance and affordability as compared to other neutralizing reagents. The problems associated with the use of this naturally occurring reagent do not only include the emission of greenhouse gases and ecological disturbances but also include a disastrous implication of depleting their reserves. To avoid these predicaments, green liquor dregs (GLD) from two Kraft pulp manufactures in South Africa were used as alternative alkaline reagents to neutralize AMD originating from Witwatersrand goldfields in Johannesburg. These GLD samples were referred to as GLD A and B. CaCO3 was used as a reference material. The GLD samples had neutralizing values that are comparable to that of CaCO3. Thus, CaCO3, GLD A, and GLD B had a neutralizing value of, 26.0, 21.2, and 21.0 % CaO respectively. Different dosages 1, 2, 6, 10, and 20 g/L of these neutralizing reagents were used to neutralize the AMD. Results of this study showed that raising the pH of AMD was possible even at a low dosages of 1 g/L. At this dosage, the acidity of the AMD sample changed from 183.36 to 21.7, 36.4, and 48.72 mg/L CaCO3, and changed the pH from 5.6 to 8.84, 8.21, and 8.0 respectively. However, the SO42- and Ec had increased from 2093 to 2360, 2538, and 2407 mg/L and from 3.6 to 4.0, 4.3, 4.2 mS/cm respectively, indicating that caution should be taken to keep these values low by keeping the reagent dosage low and being cognizant of the carbonate mineral present in GLD. The x-ray diffraction patterns of the reacted samples confirmed the presence of metal oxides and Ca and Mg compounds that were depicted by SEM/EDX micrographs. In conclusion, the results from this study showed that the pH of AMD can be raised to optimum pH process value and reduce the acidity at a low dosage, a competitive advantage over commercial CaCO3. The proposed concept can be adopted by both the mining and pulp and paper industries, for the upscaling of co-disposing GLD and AMD contaminants as an eco-friendly alternative for the CaCO3.
Beneficiation of sawdust waste in the context of an integrated forest bio-refinery mill: Kraft and pre-hydrolysis Kraft pulping properties
(UNISA, 2018) Andrew, JE; Johakimu, Jonas K; Lekha, P; Gibril, ME; Sithole, Bishop B
As part of a broader objective to extract cellulose from sawdust waste material for the production of nano-crystalline cellulose, conventional industrially available processes such as the Kraft and pre-hydrolysis Kraft (PHK) processes were investigated for delignification of sawdust produced from Eucalyptus grandis wood. In the context of the integrated forest biorefinery, it was felt that it may be useful to provide South African papermakers with preliminary data on the Kraft and PHK pulping properties of sawdust as none appeared to be available in the country. The results showed that E. grandis sawdust Kraft pulps with acceptable yields (48 %) and fibre morphologies comparable to conventional Kraft pulps, produced from wood chips, could be produced in the laboratory using typical Kraft pulping conditions. As expected, the exception was pulp strength properties such as burst, tear and tensile strengths which were 50-70 % lower than conventional pulps. During the pre-hydrolysis stage of the PHK process, up to 24 g.l-1 xylose could be removed from sawdust with minimal removal of lignin (0.1 g.l-1) and cellulose (2.5 g.l-1). Pulping of the pre-hydrolysed sawdust resulted in a pulp yield of ca. 35 %. Preliminary characteristics measured on the unbleached PHK sawdust pulp such as pentosan content (3-4 %), brightness (41 %) and viscosity (760 – 850 ml.g-1) alluded to its potential for the production of dissolving pulp.
Biowaste biorefineries in South Africa: Current status, opportunities, and research and development needs
(2023-12) Sekoa, Patrick T; Chunilall, Viren; Msele, K; Buthelezi, L; Johakimu, Jonas K; Andrew, Jerome E; Zungu, M; Moloantoa, K; Maningi, N; Habimana, O; Swartbooi, Ashton M
As one of the highest carbon-emitting nations, South Africa is working tirelessly to swiftly transition to sustainable technologies in order to strengthen its green economy initiatives. Amongst the technologies that are explored in the scientific and industrial community, biorefineries are seen as the most efficient technologies that can be used to create economic opportunities and will contribute to the advancement of a bio-based economy as they can synthesize diverse industrially-competitive products. Despite their numerous socio-economic advantages, the establishment of large-scale biorefineries in developing nations like South Africa is very scarce. Therefore, it is imperative to address the technological gaps that hinder the growth of large-scale biorefineries and provide practical solutions that could be used to solve these bottlenecks. This work provides a comprehensive review of the development of biowaste biorefinery-based technologies in South Africa. Different biowaste valorization technologies applicable to locally available organic waste streams, and the resulting market-based compounds that can be obtained from these sustainable feedstocks, are reviewed. Finally, the work provides insights into research and development needs (knowledge gaps) that should be explored by scientists and industries, as these technological solutions might propel biorefineries toward industrialization in South Africa.
Bleaching of kraft pulps produced from green liquor pre-hydrolyzed South African Eucalyptus grandis wood chips
(Arbor Publishing Ab, 2014) Andrew, JE; Johakimu, Jonas K; Sithole, Bishop B
The effect of hemicellulose pre-extraction of South African Eucalyptus grandis wood chips using green liquor, on subsequent kraft pulping and bleaching processes was studied. This was done in the context of a biorefinery mill producing both ethanol and bleached Eucalyptus kraft pulp. The pre-extraction (hydrolysis) of hemicelluloses prior to kraft pulping reduced the demand of pulping chemicals by as much as 20% and still resulted in pulps with similar kappa numbers and yields as pulps produced from unhydrolyzed wood chips (control pulps). In addition, the hexenuronic acid (HexA) content of the brownstock prehydrolyzed kraft (PHK) pulps were about 30% lower compared to the control pulps. This led to improvements in the subsequent pulp bleach-ability. Savings in chlorine dioxide for PHK pulps ranged between 2-18% for sequences that used chlorine dioxide as the primary oxidative bleaching chemical. When ozone was used in combination with chlorine dioxide, mixed results were obtained – PHK pulps showed better bleach-abilities when ozone followed immediately after oxygen delignification, i.e. OZDED or OZD(EP)D, but not when ozonation followed the acid hydrolysis (A) stage.
Extraction of hemicellulose from South African eucalyptus grandis using weak white liquor activation technology and its impact on kraft pulping efficiency
(ISWFPC, 2017-09) Johakimu, Jonas K; Sithole, Bishop B
This work summarises the findings of our research on the activation of woodchips using weak white liquor as an alternative mill self-generated alkaline solvent. The ultimate goal was to gain a better understanding on: the effectiveness of the weak white liquor in terms of wood loss, pH and concentration of the hemicellulose in the resulting extract, kraft pulping efficiency, and critical pulp and paper properties. It appears that in order to minimise wood loss and to maintain the pH of the extract, near neutral pH during woodchips activation, a short wood activation time (15 min), and weak white liquor to water ratio of 20:80 is required. The concentration of hemicelluloses in the extract was approximately 2.0 g/L. During kraft pulping, weak white liquor activated woodchips responds much faster than the control. To maintain the same kappa number as the control pulps, a 20% reduction in pulping chemicals and improvement in pulp washing efficiency of 6% are achievable. Critical pulp and hand-sheet properties of the pre-activated woodchip’s pulp samples were comparable to those of the control pulp samples. Therefore, the most attractive benefits that could be obtained from the weak white liquor woodchip activation technology are decreased mill energy demands, reduction in kraft pulping chemicals, and additional revenues from new value chains from the hemicellulose stream.
Fractionation of high Kappa number kraft pulps of the South African softwoods and sulfonating of coarse fibre enriched fraction for production of sack paper
(Appita, 2011-03) Johakimu, Jonas K; Bush, T
The focus of this study was to seek an alternative way of manufacturing sack paper with uniform quality properties at increased refining energy efficiency compared to currently applied technologies. Kraft pulp produced at Kappa number approximately to 85 was fractionated. Thereafter, the coarse fibres enriched fraction was sulphonated. Sulphonation was carried out to enhance the refinability of the coarse fibres enriched fraction. The refinability of the pulp was evaluated using PFI mill.
Fractionation of organic substances from the South African Eucalyptus grandis biomass by a combination of hot water and mild alkaline treatments
(Springer Verlag, 2015-09) Johakimu, Jonas K; Jerome, A; Sithole, Bishop B; Prabashni, L
An alternative way of fractionating lignocellulose biomass into its individual components, hemicelluloses, lignin and cellulose, was investigated. South African Eucalyptus grandis wood chips were fractionated using a combination of hot water and alkaline treatments with or without AQ. Initially, the biomass samples were treated in hot water to remove hemicelluloses. At optimum prefraction conditions, the data acquired revealed that almost 12 % of the E. grandis wood biomass could be recovered as hemicelluloses. When the hemicelluloses preextracted biomass was further treated using sodium hydroxide with or without AQ, the data indicated that the amount of lignin and cellulose that could be recovered was 22 and 36 %, respectively (as % of the wood mass). The substrate was characterised by a higher amount of a-cellulose (91–93 %), lower kappa no (12–13), viscosity (327–450 g mg/L) and DP (1078–1536). It was then presumed that such pulp could meet end-user requirement of the dissolving pulps. Industrial acceptance of this biomass fractionation concept, however, will further require careful assessments of various options for treating and purifying the hemicelluloses and lignin in their respect streams.
Government initiatives in advancing the circular bioeconomy in South Africa
(Cambridge Scholars Publishing, 2024-10) Sekoai, Patrick T; Sebogodi, Keolebogile R; Johakimu, Jonas K; Chunilall, Viren; Gbadeyan, OJ; Sekoai, P; Chunilall, Viren
The concept of a circular economy is receiving widespread attention among various stakeholders in South Africa as this scientific approach allows the management of waste streams in a sustainable and environmentally conscious manner while creating new value chains through the synthesis of high-value-added products such as fuels, chemicals, additives, etc. As opposed to the linear model that embraces the take, produce, and discard approach, the circular model embraces the recycle, reuse, and reduce approach, which involves the circularity of the wastes, leading to minimum and/or zero waste during the downstream process. Despite the various socioeconomic benefits that can be achieved from the circular biobased processes, various bottlenecks must be addressed before their full implementation. This chapter discusses the government initiatives to advance circular biobased opportunities in South Africa. The limitations that delay the progress of this technology are also discussed. The study also provides suggestions that could help fast-track the scalability of circular biobased technologies in South Africa.
Green liquor impregnation and Kraft pulping of South African Pinus Patula – “A practical approach to provide cost savings in a Kraft mill’s pulping operation”
(TAPPSA, 2011-02) Johakimu, Jonas K; Bush, T; Lucia, L
The effect of green liquor pre-treatment (GLP) on Kraft pulping of Pinus Patula has been investigated. Wood chips were pre-treated with green liquor, and subsequently subjected to Kraft pulping to achieve a target Kappa number of 65-70. The results here in have revealed that GLP has the potential to substantially improve the delignification rate during Kraft pulping. Compared to regular Kraft pulping; the H-Factor can be reduced by almost 52% when GLP is applied. In addition, if the H-Factor is maintained at the same level as was used during regular Kraft pulping, the liquor charge can be reduced by 33%. GLP followed by Kraft pulping produced pulp samples with superior strength properties to those produced by regular Kraft pulping. The potential benefits of GLP technology to the Kraft pulping industry are; providing cost savings, increased digester productivity, and mitigation of some of environmental impacts. Depending on the process economics of the pulping process of a Kraft pulp mill, GLP can be used to shortening of the digester pulping time or down sizing the limekiln requirements.
Ozone bleaching of South African Eucalyptus grandis kraft pulps containing high levels of hexenuronic acids
(Tappi Press, 2013-08) Andrew, JE; Johakimu, Jonas K; Ngema, NE
Ozone use in conjunction with chlorine dioxide during pulp bleaching offers several advantages over conventional bleaching sequences that make use of chlorine dioxide only. Despite this, in South Africa, only one mill uses ozone. The current study was a preliminary investigation into the use of ozone in bleaching sequences for kraft pulps produced from South African Eucalyptus grandis wood chips, which typically contained high amounts of hexenuronic acids (HexA). The objective of the study was to compare the performance of ozone to other technologies used to remove HexA, such as acid hydrolysis (A) and hot chlorine dioxide (DHT) stages. Bleaching sequences using chlorine dioxide (i.e OAD0ED1D2 and ODHTED1D2) were compared to bleaching sequences using ozone (i.e. OZD0ED1 and OAZD0ED1). The results showed that ozone preferentially reacted with HexA in the presence of lignin. When applied after oxygen delignification, ozone had the same HexA removal efficiencies as the A- and DHT- stages at dosages in excess of 0.6%. When used in combination with the A-stage, the HexA removal efficiencies reached 96%. Consequently, up to 15% savings in the estimated bleaching chemical costs were achieved when OAZD0(EP)D sequence was compared to the standard reference sequence OAD0ED1D2. The residual HexA in the bleached pulp affected brightness reversion of the pulps, but this was only evident for the bleaching sequences that used chlorine dioxide, and not for those that included ozone.
Preliminary study on the potential of improving pulp quality and energy efficiency in a South African TMP mill
(TAPPSA, 2010-09) Johakimu, Jonas K; Bush, T
Under the current mill refining practices, the mill is introducing too much refining energy into the fibre. The lower levels of freeness for the accept samples (18 vs. 90 CSF ml required) and the higher amounts of fines confirms this (Table 1& Fig 4). The mill’s screen fractionation process has limited efficiency. Substantial amounts of thick-walled fibres are present in the mill accept pulp samples (i.e. 66% by mass of the mill accept has a freeness of 256 ml CSF (Table 2)). The benefits of adding a Hydrocyclone to the fractionating system for TMP pulp has been demonstrated. The information revealed in the study may be used as benchmark for evaluating alternative ways of optimising the TMP process. One approach could be a single stage refining followed by a screen and Hydrocyclone fractionation.
Preliminary study on the potential of improving pulp quality and energy efficiency in a South African TMP mills
(TAPPSA, 2010-03) Johakimu, Jonas K; Bush, T
The main focus of this work was to evaluate an opportunity for product quality and refining energy efficiency improvement through assessing the current mill practices in South African TMP mills. The fractionation trials were conducted at a CSIR laboratory using Hydrocyclone. In order to provide a framework for mill process improvement, two issues were examined. Firstly, investigations focused on evaluating the pulp quality of the mill feed pulps. This work was aimed at getting a better understanding on the limitation of the mill refining process. This was accomplished by using the secondary refiner pulps (mill feed). The results data showed that under the current mill practices, the mill is introducing too much refining energy into fibres. The extremely lower value of freeness (32 ml CSF) for base fraction pulps confirmed the scenario. The second set of trials examined the efficiency of the mill fractionation process in terms of the final pulp quality. The mill’s accept pulps were fractionated. The results data indicated that the mill screens’ fractionation process has limited efficiency. A substantial amount of thick walled fibres was found in the mill’s accept pulps. Approximately 66% by mass of the mill’s accept pulps (from the 0.18 mm slotted screens) showed freeness higher than 250 ml CSF. This has a potentially negative effect on the product quality. Our preliminary study has proved that there is significant potential for Hdrocyclone fractionation in this process. This will lead to energy savings due to less intensive main line refining. In addition, the product quality will be improved due to fewer thick walled fibres and less fines in the final pulp. Fewer fines will lead to better dewatering
A review of technologies used in handling the acid mine drainage challenge: Perspectives on using green liquor dregs as a sustainable option for treatment of acid mine drainage
(2021-02) Sebogodi, Keolebogile R; Johakimu, Jonas K; Sithole, Bishop B
Acid mine drainage (AMD) is one of the repercussions that result from earth-moving activities around the sulfide-bearing mineral hosts. The detrimental effects associated with this AMD are driven by its characteristics, which include low pH and high concentrations of sulfate and toxic dissolved metals. Traditionally, the prevention and treatment of AMD are achieved by using technologies that use, amongst other, naturally occurring soils and carbonates. However, the continual use of these materials may eventually lead to their depletion. On the other hand, industrial by-products have been proven to occupying land that could have otherwise been used for profitable businesses. Additionally, the handling and maintenance of landfills are costly. In this current trend of a circular economy that is driven by industrial symbiosis, scientists are concerned with valorizing industrial by-products. One such by-product is the green liquor dregs (GLD) from Kraft mills. The neutralizing and geotechnical properties of these wastes have prompted the research pioneers to seek their potential use in handling the challenges associated with AMD. In this review, the formation AMD, trends in technologies for treatment and prevention of AMD are critically analyzed. This includes the feasibility of using GLD as an alternative, promising sustainable material.
Valorisation of mango seed via extraction of starch: preliminary techno-economic analysis
(Springer, 2017-11) Tesfaye, T; Johakimu, Jonas K; Chavan, RB; Sithole, Bishop B; Ramjugernath, D
Reducing environmental impacts and obtaining economic benefits based on utilisation of waste materials are drivers for the implementation of cleaner production policies and technologies in food processing industries. Starch is a very versatile material with a wide range of applications in the food, pharmaceutical, textile, paper, cosmetic and construction industries. In Ethiopia, starch is widely used in the textile industry. To meet the starch demand, the country imports approximately 45% of the starch used in the country. Consequently, it is imperative to find additional sources of starch that could substitute for the amount of starch that is currently being imported. Mango seeds, a waste material that is disposed of after consumption of mangos, were studied for potential use as an alternative resource for starch production. The results showed that starch extraction from mango seeds was facile and a good quality product was obtained. The present study is concerned with a techno-economic analysis for industrial production of starch from mango seeds. The study shows that extraction of starch from waste mango seeds is feasible: the project is financially viable with an accounting rate of return of 83% and a breakeven analysis of 78% with a payback period of 2 years.

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